Method of rolling metal sheets



May 31, 1932. F. E. FLYNN METHOD 0F ROLLING METAL SHEETS Filed Aug. 22,1929 .N .LL

l Patented May 31, 1932 UNITED STATES PATENT OFFICE FRANKl E. -IEIYNN,-OF WARREN, OHIO, ASSIGNOR TO REPUBLIC STEEL CORPORATION,

OF PITTSBURGH, PENNSYLVANIA, A CORPORATION F NEW JERSEY METHOD OFROLLING METAL SHEETS Application led August 22, 1929. Serial No.387,635.

My invention relates to a method of producing steel sheets and,particularly, to the production of full finished strip sheet.

Under the present practice, the strips are hot rolled and coiled, andthen pickled preparatory to cold rolling. The pickling is effected bysoaking the coiled strips in a dilute acid solution to remove theoutside scale formed during the hot rolling. The, cold 1o stripvis thenpassed through a plurality of tandem cold mill stands and coiled.Because of the fact that the strip is passed through a number ofdifferent sets of rolls, it is necessary to shape each set of rolls inorder to produce a flat strip. Even though therolls are carefullyshaped, it is necessary to pass the strip through an ironing-out roll toremove any irregularities in the surface of the strip.

The heat treatment to which the strip is subjected in the processes nowemployed consists of box annealing the strip in coils. After boxannealing the strip is temper rolled and coiled, and finally, passedthrough 5 a roller leveller and sheared into lengths.

There are a number of objectionable features in the present process. Thefirst of these has `already been mentioned, namely, that it is diicultto produce a flat sheet by passing the cold strip through a successionof of different cold mill stands and an ironingout pass is necessary..This additional pass necessitates an extra handling of the material.

, Another objection to the present method is that the strip, is boxannealed in coils. Becauseof the shape of the coils, it is impossible tostack them in the boxes efficiently and only a comparatively smallamount of strip may be placed in one box. In a representative operationit'was found impossible to place more than 12,000 pounds of steel in abox which. with its bottom, weighed 33,250

pounds. It follows that the heat eiiiciency of an operation whichrequires the continued heating of such a box to anneal the relativelysmall amount of steel therein. is very low.

I substitute for the successive cold mill stands of the present process,a singlecold mill stand through which I pass the strip .under tension,after pickling, a plurality of .times suiicient to bring about thedesired re- A duction in the gauge of the strip. In my process, thestrip is then passed through leveling rolls and sheared into lengths. Itis an important feature of this process that all steps subsequent vtothe initial cold rolling are preformed upon the material in the form ofsheets instead of long strips in coils. This features is responsible fora number ofadvantages characteristic of the process such as economichandling, eiicient treating, and the like. .The next step consists inannealing the sheets in a normalizing furnace. The normalizing treatmentconsists in heating and cooling the sheets in the presence of air. Thisstep improves the grain structure of the sheets, makes possible furthercold rolling, and is accompanied by the formation of a coat of oxide orscale on the surface of the sheet. This coat may be removed by the usualpickling process, after which the sheets are again annealed, this timein a boxannealing furnace. Because the steel to be box-annealed is inthe formYY of sheared sheets, it maybe treated more efiiciently. As anexample, it is possible to stack 36,000 pounds of steel sheets into a33,000-pound box as compared to 12,000 pounds of strip steel in coils.

Upon removal from the box-annealing furnace the sheets are again lightlypickled 'or scru bed in a suitable machine and, finally, temper rolledin a single cold mill stand.

The sequence of the operations involved in ,the method of my inventionis indicated in the accompanying drawings, in which Figure 1 is aschematic plan view of the apparatus necessary to provide theabovedescribed treatment for the strip and sheets; an

Figure 2 is a schematic elevation of the apparatus shown inFigure 1.

Referring .particularly to Figure 1, hot steel strip is supplied fromthe hot millin coils and pickled in the pickling tank 10. After thepickling process, the steel strip is passed back and forth between thereels 11 and 12 under tension, through the cold mill 100 stand 13. Onthe last pass through the cold mill stand 13, the strip is coiled bymeans of a coiler 14.

The coiled strip is next passed through a roller leveler 15 to a shear16 where it is cut into the desired lengths.

The normalizing fiirnace is indicated at 17 and the sheared sheets arepassed therethrough by means of a conveyor, after which they are againsubjected to the pickling treatment in the tank 18 to remove the scalewhich is formed in normalizing. The normalized and pickled sheets arethen given a treatment in theboX-annealing furnace 19. This step iseffected in a reducing atmosphere such as that provided by supplyingcoke-oven, natural, or charcoal gas to the annealing furnace in theknown manner. Since no oxide coat is formed on the sheets during thisstep, a light pickling or scrubbing is sufficient to prepare the sheetsfor the final cold roll, and even this treatment may be omitted. Thispickling or scrubbing treatment is applied in the tank 20.

From the tank 20, the sheets are passed to the cold mill stand 21, inwhich the sheets are temper rolled and finished.

The apparatus involved in the process above described is shown inelevation in Figure 2 and corresponding reference numerals indicatesimilar portions of the equipment.

The process of my invention is characterized by several markedadvantages over the method now in use. The first of these is a lowerunit cost which results from a higher yield or a lower percentage ofscrapped sheets. This lower percentage of scrapped sheets resultspartially from the scrubbing operation which makes it possible toreclaim a considerable percentage of steel that might otherwise bescrapped because of grease spots.

Another factor contributing to the lower cost per unit is the moreefficient handling which is made possible by the elimination of theironing-out pass. The cost of the box annealing is reduced because ofthe fact that the boxes can be more eiiiciently stacked with sheets thanwith coiled strip as indicated by examples given above.

Another advantage of the proposed method is that the product possessesmechanical characteristics superior to those of any product of thepresent method. These characteristics result from the heat treatment towhich the sheets are subjected in the normalizing and box-annealingfurnaces. There is no objection to this sequence of operations as theremight be to box annealing subsequent to the first-cold rollingoperation. In the latter case, the hard shiny surface of the cold rolledsteel sheets causes them to adhere to each other with the result thatcross breaks are formed in the sheets when they are separated uponopening the box. This difficulty is avoided in the proposed methodbecausethe normalizing treatment, followed by pickling, removes theshiny surface so that the sheets show no tendency to adhere and mayreadily be separated after box annealin Another advantage accrues om thefact that the final cold rolling is applied to the steel as sheetsinstead of as coiled strip. After annealing, the steel is in a conditionknown as dead soft and when cold rolled in coils, cross breaks in thestrip are formed which cannot be rolled out. These defects necessitatescrapping a portion of the output. The tendency to form cross breaks ismaterially lessened by finally cold rolling the product as sheetsinstead of as coiled strip.

Although I have described a specific sequence of steps for performingthe method of my invention, it is to be understood that these steps aremerely a preferred example o practicing my invention. It is not myintention to be limited to the exact steps and sequence of operationsdescribed and the only limitations to be imposed upon the scope of myinvention are those necessitated by the terms of the 'appended claims.

I claim:

1. In a method of producing steel sheets, the steps which consist inpickling coiled steel strip, passing said strip cold through a singleset of rolls a plurality of times, shearing said strip into lengths,normalizing said lengths, pickling the lengths and annealing them in anon-oxidizing atmosphere, lightly pickling and scrubbing said lengthsand passing them cold through a second set of rolls.

2. In a method of rolling steel sheets, the steps which consist inpickling steel strip in coils, reeling said strip cold, under tension,through a single set of rolls a plurality of times, shearing said stripinto lengths, heattreating said lengths, removing the scale formedthereon during said treatment, annealing said lengths in a non-oxidizinatmosphere, cleaning and again cold-ro ling them.

3. In a method of rolling steel sheets, the steps which consist inpickling steel strip, cold-rolling it under tension through one set ofrolls a plurality of times, shearing the strip into sheets, passing thesheets through a normalizing furnace, repickling the sheets, annealingthem in a box furnace, cleaning and again cold-rolling the sheets.

4. In a process for making steel sheets, the steps comprisingcold-rolling pickled steel strip under tension a plurality of times ina. single set of rolls, shearing said strip into sheets, normalizingsaid sheets, pickling and annealing them in a box furnace and againcold-rolling said sheets.

5.' In a process for the cold-working of steel, the steps includingcold-rolling, normalizing, pickling, annealing and again coldrolling. K

6. In a method of making sheets, the steps consisting in normalizing thesheets, pickling the sheets and box-annealing them.

7. In a method of making sheet metal, the steps consisting incold-rolling a metal strip under tension through a single set of rolls aplurality of times, shearing the strip, normalizing the sheets produced,pickling and annealing the sheets in the absence of oxygen, cleaning thesheets and finally cold-rolling them again.

8. In a metal-Working process, the method which consists in cold-rollingmetal strips into sheets by passing said strips repeatedly through asingle set of'rolls, under tension, normalizing the sheets, annealingthem in the absence of oxygen and again cold-rolling them.

9. In a method of producing sheets, the steps consisting in cold-rollingstrip metal, shearing the strip into sheets, heat-treating said sheets,annealing them in a slightly7 reducing atmosphere and again cold-rollingthem.

10. In a metal-working process, the steps consisting inY cold-Working amass of metal heat-treating it, annealing it in a reducing atmosphereand again cold-working it.

11. In a heat-treating process for sheet steel, the steps including'heating the sheets in an oxidizing atmosphere, pickling the sheets andannealing them in a non-oxidizing atmosphere.

In testimony whereof I have hereunto set m hand.

y FRANK E. FLYNN.

